An innovative form of “flat pack” construction can slash the time and cost required to build concrete arch-shaped bridges while also greatly increasing their durability and projected lifespan.
While "flat pack" assembly systems are more commonly associated with DIY cupboards, kitchens and household furnishings, civil engineers are now applying this elegant construction method to the venerable arch bridge, in order to dramatically reduce building times and maintenance requirements.
Engineers from Queen's University Belfast are currently working on the development of the world's longest "flat pack" arch bridge which is made using pre-cast concrete materials.
The bridge that is scheduled for construction over Wallington River just outside of Portsmouth in Hampshire will measure 16 metres in length and consist of 17 tapered pre-cast concrete units that are connected together by a flexible polymeric membrane. Each of of the pre-cast concrete units measures a metre in width and weighs 16 tons.
The bridge, the design of which employs the university's patented FlexiArch system, will be conveyed to the site in its original flat pack form, before being lifted into place and converted by the force of gravity into the desired arch structure.
The connecting membrane ensures that all the pre-cast units are kept in place initially as the crane deposits the structure, before gravity compels each of the segments to lock in against its neighbour. The arch is then secured in position, and concrete infilling and roadway levelling is performed.
The chief advantages of the flat pack construction method lie in the areas of convenience, time savings and cost. The Wallington River Bridge will be installed within a day, using no more equipment than a 200 to 300-ton crane and a purpose-built lifting beam for the concrete modules.
"[The bridge] is exceptional as it is easily transported in flat pack form and then rapidly installed on site," said Abhey Gupta, project manager with Macrete Ireland, the pre-cast concrete company that developed the bridge in collaboration with civil engineers from Queen's University Belfast.
This compares to the multiple months it would take to build a conventional arch bridge of similar dimensions using traditional methods, incurring far greater labour and construction costs.
Another key advantage of the flat pack bridge is its durability. According to Gupta, the FlexiArch bridge has a projected operating life of as long as three centuries, as compared to the 120-year lifespan of its conventional peers.
The bridge achieves this enhanced longevity because its strength does not rely upon corrodible forms of reinforcement - a feature which also slashes maintenance requirements.
The concept of flat pack bridge building, which was first patented in 2004 by professor Adrian Long from the School of Planning, Architecture and Civil Engineering at Queen's University, is the product of 10 years of research starting that first commenced the early 1990s.
More than 50 of the flat pack structures have since been built throughout Britain over the past decade, including bridges at Northern Ireland's Newtownabbey Council, Gloucestershire in south-west England, and Sheinton near Wales.